Abrasion wear warning device for vehicle brakes

ABSTRACT

The present invention provides an abrasion wear warning device for indicating when a predetermined wear point has been reached in a monitored part undergoing wear by abraision, comprising a sensor means which is generally closed and part of an indicator circuit, but which upon wear of the monitored part to the predetermined wear point is opened thereby causing an indicator to be activated and to produce some visual, audible or other sensible reaction display to warn that the predetermined wear point in the monitored part has been reached.

United States Patent Rees 1151 r 3,660,815 1451 May 2, 1972 [54]ABRASION WEAR WARNING DEVICE FOR VEHICLE BRAKES I [72] Inventor: DonaldW. Rees, 12912 Leisure, Warren,

. Mich. 48095 22 Filed: Dec. 15, 1969 21 Appl. No.: 885,170

[52] US. Cl. ...340/52 A, ZOO/61.41 [51] Int. Cl. ..G08b 21/00 [58]Field of Search ..340/52, 52 A, 52 B, 244, 269;

[56] 4 References Cited UNlTEDSTATES PATENTS 3,456,236" 7/1969Labartinoetal. "340/52 3,312,936 4/1967 l-luntzinger ..340/s9 3,461,4478/1969 Marouby ..340/244 Primary Examiner-Alvin l-l. WaringAttorney-Arthur L. Girard ABSTRACT The present invention provides anabrasion wear warning device for indicating when a predetermined wearpoint has 1 7 Claims, 6 Drawing Figures PATENTE-DW 2 I913 I+ III PIC-5.6

INVENTOR.

DOA A10 IV. [[115 MMXJM ATTORNEY ABRAS ION WEAR WARNING DEVICE FORVEHICLE R KE The present invention relates to a novel abrasion wearwarning device and more particularly to such a device for indicatingwhen vehicle or other mechanical brake lining wear has reached apredetermined stage.

In the prior art, one of the most trying problems in determining when acritical wear state in an abrasion wearing part had been reached was thediscovery of a method for making this determination without thenecessity for complete disassembly. of the wearing apparatus forpurposes of visual or physical measurement inspection of the wearingpart. Probably the best known example of such a problem and that whichcosts nearly every corporate, governmental and individual entity themost time and money annually is the problem of determining when vehiclebrake linings of either the shoe or pa type have reached their criticalwear state without complete, costly and complicated total disassemblyand, generally, reassembly without replacement, of the entire wheel andbrake apparatus before the clearly audible squeeking or screechingwarning which indicates overwear and most generally extensive andexpensive brake drum or disc damage occurs.

Numerous devices have been devised to solve this problem. The majorityof these prior art devices are of two types. The first type calls forthe installation of one contact in the brake lining at the point wherewear indicates that the brake lining should be changed while the brakedrum or disc is made the other contact in a powered circuit whichincludes an indicator of one king or another. Thus, when the desireddegree of wear is reached, contact is made between the drum and theembedded contact closing the circuit and activating the indica? tor.

A second type of prior art device is one which measures the take-up ordistance which the shoe and lining must travel to engage the brake drumin a conventional shoe-in-drum type brake.

Both of these systems are useful, however, both have definiteshortcomings. In the case of the former contact systems wet brakelinings, particularly when combined with winter operations wherein largequantities of saltwater permeate the lining material often cause falseindications of ex- 1 cessive wear which require unnecessary disassemblyvery similar to that required for visual inspection. Thus, although thedevice, is useful under ideal conditions ofoperation, its use is limitedand provides only unreliable indication of brake -wear.

The use of the second type of. device described above is limited toshoe-in-drum type brakes and hence is inapplicable to disc brakes or anyother wearing part which does not operate in the same fashion as suchbrakes.

Furthermore, with the recent increased emphasis on safety and the callfor automotive equipment which provides increased security forautomobile users, the time is imminent when a simple and reliable systemfor indicating when brake lining or pad wear has reached a critical andtherefor hazardous stage will be required in automobile manufacture tosupplement the hydraulic pressure warning devices presently in wideusage. Thus, in addition to the. convenience and economic factorsinvolved in the use of a wear warning device, a safety factor is alsopresent which may in the last instance prove to be the best reason forthe development of such a device.

Thus, prior to the present invention, the brake lining of whatever shapeor form had to be visibly inspected to determine if wear limits had beenexceeded even when. a wearing warning device of doubtful reliability wasused. Inspection generally involved disassembly and removal of thevehicle wheel and the brake drum or disc caliper pad and, since liningwear varies with driver habits, driving conditions, type of liningmaterial and brake and vehicle design, visual inspection of linings hadto be performed often to insure against damage to the disc or drum dueto excessive wear even when the aforementioned unreliable devices wereemployed. This problem therefore, remains one of the most frequentlyencountered and costly problems of vehicle maintenance.

It is therefore an object of the present invention to provide animproved simplified and totally reliable method for determining whencritical or other predetermined amounts of brake lining or for thatmatter any other abrasive wear has reached a predetermined stage, and toprovide remote indication of such wear to the vehicle or other equipmentoperator without the necessity for even partial disassembly of the brakeor other wearing part.

Other objects and advantages of the present invention will be madeobvious to those skilled in the art when the following description isconsidered in relation to the accompanying drawings of which:

FIG. 1 is a side view of the sensor portion of the device of the presentinvention;

FIG. 2 is a top plan view of the sensor portion of the device of thepresent invention;

FIG. 3 is a cross-sectional view of a typical installation of the sensorportion of the device of the present invention in a brake lining of theshoe type;

FIG. 4 shows a schematic diagram of one embodiment of the electricalcircuit of the warning device of the instant invention;

FIG. 5 shows an alternative embodiment of the electrical circuitsuitable for use in the warning device of the instant invention; and

FIG. 6 shows a further alternative embodiment of the electrical circuitof the warning device of the present invention.

According to the present invention, there is provided an abrasion wearwarning device comprising a sensor means and an indicator meansconnected by circuit means and adapted for connection to a power source,said sensor means normally being closed and therefore part of thecircuit means, however, said sensor means becoming open and thereforeremoved from said circuit means when a predetermined degree of wear isexperienced by an article whose abraison wear is being monitored withthe device and the indicator means providing a readily detectableaudible, visual or other sensible display when the sensor means is soremoved from the circuit means.

More specifically, the invention provides a sensor element in circuitrelation with an indicator means which sensor means at some point at ornear the critical wear stage or any other predetermined wear point in aabrasion wearing element being monitored begins to undergo asimultaneous abrasion wearing which, at the point where the monitoredelement reaches its critical or other predetermined wear stage,undergoes a change which removes the sensor element from the circuitmeans of the warning device thereby causing the indicator means in thecircuit to be activated and to produce a warning signal of one type oranother. I

As shown in greater detail in the drawings, the sensor element 10consists basically of a small spool or other useful configuration of aninsulative material 12 through which a loop 14 of a length of asuitablecopper, aluminum or other conductive wire 16 which loop has beenformed by passing wire 16 through apertures 18 and 20 in insulator 12.The loop 14, as described hereinafter, is adapted to be electricallyconnected into an indicator circuit.

For purposes of simplicity and clarity, the description of the wearwarning device which follows will be made in relation to a brake liningapplication, however, it should be understood that the device issimilarly applicable to an almost unending list of other applicationswherein the detection of excessive or limited abrasion wear is desirableor necessary.

Installation of the sensor element into. a typical brake apparatus isshown in FIG. 2. An aperture 22 is provided in brake shoe 24 forinsertion of the sensor 10 into brake lining 26. The sensor 10, in theembodiment shown, is mounted in a recess 28 in lining 26 and a flange29on sensor 10 is provided to prevent the same from passingthrough-aperture 22, which, in addition to providing passageforextension 12 of sensor 10, simultaneously provides access for wire 16 toloop 14 within the body of lining 26.

In operation, as the brake drum 27 wears the lining 26 away, iteventually reaches the top of loop 14 and begins to wear it away also.Eventually, the wire loop 14 (or any other suitably shaped segment ofwire 16) is worn through causing the sensor element 'to open and, asexplained more fully hereinafter, activating an indicator element 33which is connected to the sensor by circuit 30 shown in FIGS. 4-6.

FIG. 4 shows one embodiment of a circuit suitable for use in the device-of the instant invention. As shown therein, the completed circuitconsists of sensorelement 10, described in detail above, an indicator33, in this case, a lamp although any other audible, or visual displayunit might be used, and a power source 32 all connected by circuit 30.Circuit 30, in addition to the elements already mentioned, also includesa first resistor means 34 and a second resistor means 36. Thus, thecircuit consists basically of an indicator 33, and a sensor 10 inparallel across a suitable power supply 32. When the sensor is closed,i.e., loop 14 is whole, the current supply flows through both theindicator and the sensor. By proper adjustment of resistors 34 and 36,for example resistor 34 has a value of ohms and resistor 36 a value of 3ohms, most of the current can be made to flow through sensor 10 whilethe current through indicator lamp 33 is limited to a value insufiicientto cause the lamp to light. When sensor 10 is opened, because of wear ofloop 14 as described above, and is therefore removed from circuit 30,all of the current flows through indicator 33 causing it to light.

In vehicle applications, power source 32 will generally comprise a 6 or12 volt DC battery, although, of course, the device is adaptable for usewith almost any direct or alternating current power source with onlyminor adjustment in the circuitry and elements thereof being required.

Alternative embodiments of circuits suitable for use in the warningdevice of the instant invention, both of which make use of switchingmeans to cause activation of the indicator means when the sensor meansis opened, are shown in FIGS. 5 and 6.

In the embodiment of FIG. 5, the circuit consists of indicator lamp 33similar to that used in the circuit of FIG. 4, and a semiconductor 40 inseries circuit relation across a power supply 32 of the type used inFIG. 4. A resistor 44 and a wear sensor 10 similar to that used in thecircuit of FIG. 4, are utilized to provide a bias voltage onsemiconductor 40 which acts as a switch. The bias voltage preventssemiconductor 40 from passing current when sensor 10. is closed,however, when sensor 10 is opened because of abrasive wear loop 14 asdescribed above, the bias voltage on the semiconductor 40 changesallowing it to pass current through the lamp or other indicator means33, thus giving an observable and detectable display of sensor openingand hence achievement of critical or other predetermined wear stage inthe monitored brake lining or other part.

FIG. 6 illustrates yet another circuit which can be used to provide thewear warning described above. In the circuit of FIG. 6, a siliconcontrolled rectifier 48 is utilized in series with indicator element 33in this case again a lamp similar to that used in FIGS. 4 and 5.Additionally, a first resistance means 52 and a second resistance means54 in parallel with rectifier 48 and indicator 33 are used. Whenproperly adjusted, resistors 52 and 54 bias silicon controlled rectifier48 preventing current flow through indicator 33 when sensor 10 isclosed. When sensor 10 is opened by virtue of loop 14 thereof being wornthrough by the abrading surface, the bias potential of the siliconcontrolled rectifier gate is increased causing silicon controlledrectifier 48 to conduct and indicator element 33 to produce its display.The circuit also includes a suitable power supply 32 as a source ofcurrent.

Thus, in the alternative circuits of FIGS. 5 and 6 a switching means isintroduced into the sensing circuit which permits activation of theindicator means upon opening of the sensor.

An alternative application of the basic principle and device of thepresent invention comprises the installation of a plurality of thesensors at various levels in the wearing monitored part so that adetermination of percent of wear could be made as the part undergoesabrasive wear. Forexample, three sensor elements could be implanted inthe wearing part in such a fashion that one of them is triggered at 25,50 and percent of useful wear and a sensible display, which could beshut off, produced at each of these levels.

As already mentioned, although the wear warning device has beendescribed primarily in conjunction with a brake lining application, ithas numerous other areas of usage including but not limited to warningof excessive wear in shafts, bearings, sliding surfaces, tires andgenerally in all other mechanical parts where undetected excessiveabrading wear poses a problem.

The invention had been described in detail with particular reference topreferred embodiments thereof, but it should be understood thatvariations and modifications thereof can be effected within the spiritand scope of the invention.

lclaim:

1. An apparatus for indicating when a predetermined wear point has beenachieved in a monitored part having wearing and non-wearing portions andundergoing wear by abrasion comprising:

a replaceable sensor element of an insulative material designed forinsertion into a recess in the non-wearing area of said monitored partextending into said wearing area and having a severable wiretherethrough to form a loop thereon on the portion of said sensorelement closest to the surface of said wearing portion;

indicator means connected to said sensor element by a single electricalcircuit having no moveable mechanical parts and adapted to be connectedto a power source;

said severable wire nonnally being whole and therefore part of saidcircuit under conditions of normal operation, however, said wirebecoming open and therefore removed from said circuit when saidpredetermined wear point has been achieved by said monitored part;

severance of said wire causing activation of said indicator means toprovide a sensible display that said predetermined wear point has beenachieved.

2. The device of claim 1 wherein said circuit means includes a firstresistor means in series circuit relation with said indicator means andsaid sensor means,'and a second resistor means in series circuitrelation with said sensor means and in parallel circuit relation withsaid indicator means, said first and said second resistor means beingadjusted such that substantially all of any current which is applied tosaid circuit means passes through said sensor means when said sensormeans is closed, and all of said current which may be applied to saidcircuit means passes through said indicator means when said sensor meansis open.

3. The device of claim 1 including a switching means which activatessaid indicator means when said sensor means achieves an open conditiondue to said monitored part achieving said predetermined wear condition.

4. The device of claim 3 wherein said switching means is asemiconductor. 5. The device of claim 4 wherein said sensor means and aresistance means are connected in parallel circuit relation with saidsemiconductor by said circuit means and said indicator means to providea bias voltage which prevents said semiconductor from passing current tosaid indicator means when said sensor means is closed, and permits saidcurrent to flow to said indicator means when said bias is altered byopening of said sensor means.

6. The device of claim 3 wherein said switching means comprises asilicon controlled rectifier in series circuit relation with saidindicator means.

7. The device of claim 6 wherein said circuit means includes a first anda second resistor means in parallel circuit relation with said rectifierand said indicator means, said first and said second resistor meansbiasing said silicon controlled rectifier so as to prevent a flow ofcurrent therethrough when said sensor means is closed, the biasingpotential of said silicon controlled rectifier being increased causingsame to conduct said current and activate said indicator means when saidsensor means is opened.

1 III 4 I

1. An apparatus for indicating when a predetermined wear point has beenachieved in a monitored part having wearing and nonwearing portions andundergoing wear by abrasion comprising: a replaceable sensor element ofan insulative material designed for insertion into a recess in thenon-wearing area of said monitored part extending into said wearing areaand having a severable wire therethrough to form a loop thereon on theportion of said sensor element closest to the surface of said wearingportion; indicator means connected to said sensor element by a singleelectrical circuit having no moveable mechanical parts and adapted to beconnected to a power source; said severable wire normally being wholeand therefore part of said circuit under conditions of normal operation,however, said wire becoming open and therefore removed from said circuitwhen said predetermined wear point has been achieved by said monitoredpart; severance of said wire causing activation of said indicator meansto provide a sensible display that said predetermined wear point hasbeen achieved.
 2. The device of claim 1 wherein said circuit meansincludes a first resistor means in series circuit relation with saidindicator means and said sensor means, and a second resistor means inseries circuit relation with said sensor means and in parallel circuitrelation with said indicator means, said first and said second resistormeans being adjusted such that substantially all of any current which isapplied to said circuit means passes through said sensor means when saidsensor means is closed, and all of said current which may be applied tosaid circuit means passes through said indicator means when said sensormeans is open.
 3. The device of claim 1 including a switching meanswhich activates said indicator means when said sensor means achieves anopen condition due to said monitored part achieving said predeterminedwear condition.
 4. The device of claim 3 wherein said switching means isa semiconductor.
 5. The device of claim 4 wherein said sensor means anda resistance means are connected in parallel circuit relation with saidsemiconductor by said circuit means and said indicator means to providea bias voltage which prevents said semiconductor from passing current tosaid indicator means when said sensor means is closed, and permits saidcurrent to flow to said indicator means when said bias is altered byopening of said sensor means.
 6. The device of claim 3 wherein saidswitching means comprises a silicon controlled rectifier in seriescircuit relation with said indicator means.
 7. The device of claim 6wherein said circuit means includes a first and a second resistor meansin parallel circuit relation with said rectifier and said indicatormeans, said first and said second resistor means biasing said siliconcontrolled rectifier so as to prevent a flow of current therethroughwhen said sensor means is closed, the biasing potential of said siliconcontrolled rectifier being increased causing same to conduct saidcurrent and activate said indicator means when said sensor means isopened.